Myocardial Infarction Pathophysiology, Studies and Treatments

Myocardial Infarction

The heart needs a consistent supply of oxygen and nutrients.  Three coronary arteries are found in the heart, with two of them branching out to deliver oxygenated blood to the heart.  Blockage in one of these arteries or branches causes part of the heart to be starved of oxygen.  This is referred to as cardiac ischemia.  If this ischemia continues over a lengthy period of time, the starved heart tissue dies and this is known as a heart attack.  In medical terms, a heart attack is called a myocardial infarction, which translates to “death of heart muscle.”  According to the World Health Organization, in order for a patient to be diagnosed with a myocardial infarction, they must present with at least two of the following three criteria:  clinical history of chest discomfort associated with ischemia (chest pain), an elevation of cardiac blood markers (Troponin-I, CK-MB and myoglobin) and changes on electrocardiographic tracings (taken serially).

PATHOPHYSIOLOGY

The majority of heart attacks are the result of coronary artery disease known as atherosclerosis, or hardening of the arteries, a condition that clogs coronary arteries with calcified, fatty plaques over time. This buildup, or atherosclerosis, develops over many years.  The trigger for a heart attack is often a blood clot which blocks blood flow through a coronary artery.  It is now believed that the less severe plaques are the ones that cause most heart attacks.  The milder blockages  rupture and then cause the blood clot to form.  These blood clots, depending on size, can partially or completely block blood flow to the heart. 

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Most myocardial infarctions occur during several hours.  Severe heart attack pain if often described as if a the heart is being squeezed by a giant fist.  Mild heart attacks could be mistaken for heartburn and the pain may be intermittent or constant. Shortness of breath, faintness, dizziness or nausea are other signs and symptoms of a heart attack. The classic symptoms of chest pain are often less likely felt in women.  Instead women may feel pain in their neck, arm, jaw or back.  Women may also feel a sense of fullness in their chest.

Myocardial infarctions are the result of major risk factors stemming from coronary artery disease or coronary heart disease.  Some modifiable risk factors include high blood pressure, high cholesterol, high blood sugar, obesity, smoking and a sedentary lifestyle as well as illegal drug use. Stress is also a risk factor due to exertion and excitement that may trigger a heart attack.  Other risk factors that are non-modifiable include age (the risk increases with age), a family history of early heart attack and autoimmune disorders such as rheumatoid arthritis and lupus.  Pre-eclampsia during pregnancy is also a non-modifiable risk factor.

There are no previous warning signs in about 25% of all heart attacks due to “silent ischemia”, which are sporadic interruptions of blood flow to the heart.  These interruptions are usually pain-free but they can damage the heart tissue. ECG (electrocardiogram) testing  can detect silent ischemia.  Stroke, irregular heartbeats (persistent heart arrhythmias), formation of blood clots in the legs or heart, heart failure and aneurysms are serious complications.  Diabetics often have silent ischemia. 

A chance of full recovery stands in patients who survive the initial heart attack and do not exhibit major problems a few hours later.  Because a heart attack does weaken the heart to some degree, recovery is a delicate process, however, generally a normal life can be resumed. 

LABORATORY STUDIES

 Several laboratory studies are used to diagnose a myocardial infarction.  The primary diagnostic studies are an electrocardiogram (ECG) and a serum cardiac biomarker (cardiac-specific troponin).  Other laboratory studies may include CK-MB test (creatine kinase enzyme), C-Reactive Protein test, homocysteine test, b-Type natriuretic peptide marker and NT-Pro-BNP. 

 The cardiac-specific troponin test is a blood test that measures the levels of troponin T or troponin I proteins in the blood. Troponin T and I are released when the heart muscle has been damaged, such as when a heart attack occurs.  The greater the amount of troponin T and I in the blood, the more damage there is to the heart.  Patients should be educated that no special steps are needed to prepare for this test, however, explaining the purpose of this test should be included in patient teaching.  The patient should be educated that the most common reason this test is performed is to see if a heart attack has occurred or if chest pain and other signs of a heart attack have been experienced.  The test may also be ordered if there is presence of angina that is getting worse but there are no other signs of a heart attack and it may also be done to help detect and evaluate other causes of heart injury.  Explanation to the patient should also include that this test is usually repeated two more times over the next 6 to 24 hours.  The patient should also be told that, as with many blood tests, a slight pain or a sting when the needle is inserted will be felt as well as possible throbbing at the site after the blood is drawn. 

 Damage to the heart will be determined with even a slight increase in the troponin level with very high levels of troponin indicating that a heart attack has occurred.  Increased troponin levels within six hours occur in most patients who have had a heart attack and almost all patients who have had a heart attack will have raised levels of troponin after 12 hours.  For one to two weeks following a heart attack, troponin levels may remain high.

DIAGNOSTIC STUDIES & TREATMENTS

An electrocardiogram, or ECG, study will be also be done.  It records the timing and strength of the electrical impulses generated by the heart and sometimes referred to as a 12-lead EKG or 12-lead ECG because information is gathered from 12 different areas of the heart.  This information is viewed by electrodes placed on a person’s chest and sometimes limbs and recorded on a graph as waves.  Different patterns will display that correspond to each electrical phase of each heartbeat.  Abnormal heart rhythms will show on an ECG if they occur during the test.  The presence of an ST segment elevation on the ECG is one of the most significant findings of a myocardial infarction. Pathological Q waves can also be an indication of a myocardial infarction but their presence does not always suggest that a new myocardial infarction is occurring.  Patients should be informed that an ECG is a painless procedure.  Other procedures that may be necessary based on the findings of primary tests can include an exercise stress test, Holter monitor, chest x-ray, radionuclide imaging, echocardiography, cardiac catheterization and coronary angiography. 

MEDICATIONS

There are numerous medications that can be prescribed for a person who has suffered a myocardial infarction.  Anticoagulants decrease the clotting ability of the blood.  Possible side effects of anticoagulants include syncope, weakness and abdominal cramps.  Aspirin may be prescribed to preventive plaque buildup and some patients may be prescribed another antiplatelet drug in combination with aspirin.  This is referred to as dual antiplatelet therapy (DAPT).  Possible side effects of aspirin include gastrointestinal bleeding, nausea and vomiting.  Angiotensin-Converting Enzyme (ACE) Inhibitors help expand blood vessels and decrease resistance by lowering levels of angiotensin II, which allows blood to flow more easily to make the heart more efficiently.  Side effects of this medication may include dry cough, hyperkalemia and fatigue.  Angiotensin II Receptor Blockers, or ARB’s, prevent angiotensin II from having any effects on the heart and blood vessels rather than lowering levels of angiotensin II, as ACE inhibitors do.  This prevents increases in blood pressure.  Side effects of ARB’s can include headache, dizziness and low blood pressure.  Another common medication is a beta blocker which decreases the cardiac output and heart rate, lowering blood pressure and making the heart beat with less force.  Beta blockers can produce side effects such as drowsiness or fatigue, cold hands and feet, and dry mouth, skin, or eyes.  Calcium channel blockers are another common medication.  This medication hinders the movement of calcium into the cells of the heart and blood vessels, which may decrease the heart’s pumping strength and promote relaxation of blood vessels.  Constipation, edema of the feet, ankles and legs, and increased appetite are some common side effects of calcium channel blockers.  Digitalis preparations such as Digoxin may be prescribed, especially if the patient is not responding to ACE inhibitors and diuretics.  This medication increases the force of the heart’s contractions.  This can be helpful in irregular heartbeats, heart failure and to slow some types of arrhythmias, particularly atrial fibrillation.  Digitalis preparations can produce common side effects such as mood and mental alertness changes including confusion and depression as well as anxiety.  Other medications that may be prescribed are cholesterol lowering medications, diuretics and vasodilators. 

Medications should be administered with careful consideration of adverse effects with other medications and certain foods.  For example, grapefruit decreases the effectiveness of Digoxin and beta blockers should not be taken with calcium channel blockers.  A person’s current or pre-existing condition should also be considered including any allergies and that the medication prescribed is appropriate to treat the patient’s condition without compromising or worsening other aspects of the person’s health.  The Six Rights of Medication Administration should be verified each time the medication is administered to prevent a medication administration error.

NUTRITION AND DIET

When a person survives a myocardial infarction, there are vast dietary changes.  Plenty of vegetables, fresh fruit, wholegrain breads, cereal, pasta, rice and noodles and lean meat are encouraged.  One should include two to three servings of fish and seafood every week. There is great emphasis on the limiting of processed meats, fast or convenient foods such as pizza, pastry and hamburgers.  Excess salt is discouraged and if possible, ‘no added salt’, ‘low-salt’ or ‘reduced salt’ foods are preferred.  Exercise is also emphasized.  Even walking 30 minutes several days a week is beneficial because it improves cholesterol levels, lowers blood pressure, reduces the risk of more heart problems and is low impact. 

CULTURAL AND HERITAGE

Barriers in health care abound.  Communication and language barriers, lack of proper transportation to a health care facility, financial instability and adherence to strict cultural and heritage customs are a few examples.  After a myocardial infarction, many people feel compelled to resume job roles immediately out of fear of losing employment or due to financial strain.  Interpreters must be utilized to break the communication and language barriers and transportation arrangements can be made for patients to adhere to the proper care that follows a myocardial infarction.  However, cultural customs can pose a great barrier in the treatment of a patient suffering a myocardial infarction.  For examples, Asian-Americans seem less likely to accept care due to traditions of herbal remedies.  Many cultures have a distrust in the hospital system and Western medicine.  Therefore, these cultures are less likely to be open to treatment during or after a myocardial infarction.  Of those that do receive treatment for myocardial infarction, many simply do not adhere to follow up care.  Interventions need to include patient teaching on the risks for refusal of treatment following a myocardial infarction. 

NURSING PROCESS

 The nursing process encompasses the following elements:  assessment, diagnosis, planning, implementing and evaluating.  The first step, assessment, is the gathering of information about a patient’s physiological, psychological, spiritual and sociological status through interviews and physical examinations.  The second step, diagnosis, is where an educated judgment about a potential or actual health problem about a patient is made and is an important step in determining a patient’s course of treatment.  The third step, planning, is developed when a patient and nurse agree on the diagnoses.  It is a plan of action and multiple diagnoses can be addressed.  These diagnoses are prioritized with severe symptoms and high-risk factors getting priority.  In the planning step, measurable goals are created for the patient.  The fourth step, implementing, involves a follow through on the decided plans of action which is patient specific and focuses on achievable outcomes.  The implementation step can range from hours to months.  The final step, evaluating, is complete when the goals for patient wellness are met.  If it is determined that the patient has not improved or if the goals were not met, then the nursing process must begin again from the assessment step.

 The following diagnoses can be assigned and implemented for the patient with a myocardial infarction.

 Acute Pain related to myocardial ischemia as evidenced by facial expression of pain – an intervention for this would be to obtain a pain description from the patient including intensity (on a scale of 0–10), location, duration, characteristics (crushing, dull, sharp) and pain radiation. The rationale for this diagnosis is that pain is a subjective experience as described by the patient. Pain is what the patient says it is and can be difficult to diagnose. Documenting the patient’s pain description helps to determine effectiveness of treatment by comparing it to ongoing assessments.

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Activity Intolerance related to imbalance between oxygen supply and demand as evidenced by abnormal heart rate or blood pressure response to activity – an intervention for this diagnosis would be to assess the patient’s heart rate and blood pressure before, during and after activities.  The rationale would be to establish short and long term goals as well as therapies needed. 

Fear related to threat of death as evidenced by increased questioning – a proper intervention would be to assess the level and cause of the fear for the rationale of determining therapies needed.  The patient may fear the diagnostic studies being performed, the pain being experienced, being separated from loved ones or being in the hospital setting itself and proper treatment and therapies can be established based on the assessment of the patient’s fear or fears.

Risk for decreased cardiac output – an intervention for this diagnosis would be to monitor the patient’s respiratory rate, rhythm and breath sounds for the rationale of assessing for rapid and shallow respirations and the presence of crackles and wheezes that are characteristic of decreased cardiac output. 

Risk for ineffective myocardial tissue perfusion – an intervention for this diagnosis would be to monitor the patient’s cardiac rhythm by noting any changes on the 12-lead ECG.  The rationale for this is that cardiac rhythm changes can occur secondary to myocardial ischemia and monitoring for changes will reduce the risk of harm to the patient.

Risk for ineffective coping – an intervention would be to assess the patient’s specific stressors for the rationale of developing coping strategies.  The myocardial infarction patient may have concerns of being unable to resume normal activities or maintain the new lifestyle changes that come after a myocardial infarction.

Deficient Knowledge related to insufficient information as evidenced by inaccurate follow-through of instruction – an intervention would be to assess the patient’s knowledge of the cause of a myocardial infarction, its treatments and recovery process.  The rationale for this would be to provide proper education and address or rule out any misconceptions the patient may have regarding his or her diagnosis.

Risk for electrolyte imbalance – an intervention for this diagnosis would be to monitor and document lab data such as sodium, potassium, chloride, magnesium and calcium levels as well as ECG changes.  The rationale is that serum electrolyte levels are decreased due to fluid shifts and ECG changes such as a ST-segment changes are seen with electrolyte imbalances.

Risk for impaired gas exchange – an intervention for this is to assess the patient’s breath sounds for decreased ventilation and the presence of adventitious sounds.  The rationale is that diminished breath sounds associated with poor ventilation as well as changes in breath sounds can reveal impaired gas exchange.

 Risk for ineffective health management – an intervention would be to determine risk factors that may affect the patient’s adherence to the treatment regimen and to include the patient in the treatment planning regimen.  The rationale is to define factors such as lack of financial resources, lack of social support, beliefs and values that impede the treatment regimen and any past history of noncompliance to help direct proper interventions.

SUMMATION

 With proper health maintenance, a myocardial infarction can be prevented.  Many lifestyle factors are modifiable and, if kept under control, can benefit a patient even if he or she has already experienced a myocardial infarction before.  Education and training are critical when handling a patient who is experiencing a myocardial infarction because the proper treatments can be established to save a person’s life.  Knowing what changes to look for in a patient’s health status, medications administered and their side effects, collaborating with various team members and the patient on a treatment regimen are only a few of the many key points that are crucial in a myocardial infarction patient.  After a patient survives a myocardial infarction, there are still many items to address such as a modified lifestyle, how the patient perceives his or her modified lifestyle, the likelihood that the patient will adhere to the medication regimen, financial and social support and follow up care.  All of these important factors fall on the nurse and it is his or her responsibility to ensure that the patient receives the best care possible during and after a myocardial infarction.  That process starts with being knowledgeable about what a myocardial infarction is, how it can be prevented, how to act when handling a patient suffering a myocardial infarction and what to plan for in the after care. 

REFERENCES

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